title: Host-guest chemistry from solution to the gas phase: an essential role of direct interaction with water for high-affinity binding of cucurbit[n]urils.
abstract: An investigation of the host-guest chemistry of cucurbit[n]uril (CB[n], n = 6 and 7) with α,ω-alkyldiammonium guests (H2N(CH2)xNH2, x = 4, 6, 8, 10, and 12) both in solution and in the gas phase elucidates their intrinsic host-guest properties and the contribution of solvent water. Isothermal titration calorimetry and nuclear magnetic resonance measurements indicate that all alkyldiammonium cations have inclusion interactions with CB[n] except for the CB[7]-tetramethylenediamine complex in aqueous solution. The electrospray ionization of mixtures of CB[n] and the alkyldiammonium guests reflects their solution phase binding constants. Low-energy collision-induced dissociations indicate that, after the transfer of the CB[n]-alkyldiammonium complex to the gas phase, its stability is no longer correlated with the binding properties in solution. Gas phase structures obtained from density functional theory calculations, which support the results from the ion mobility measurements, and molecular dynamics simulated structures in water provide a detailed understanding of the solvated complexes. In the gas phase, the binding properties of complexation mostly depend on the ion-dipole interactions. However, the ion-dipole integrity is strongly affected by hydrogen bonding with water molecules in the aqueous condition. Upon the inclusion of water molecules, the intrinsic characteristics of the host-guest binding are dominated by entropic-driven thermodynamics.
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Republic of Korea.
authors.forename: Shin Jung C
authors.initials: SJ
authors.lastname: Lee
authors.forename: Jong Wha
authors.initials: JW
authors.lastname: Lee
authors.forename: Hong Hee
authors.initials: HH
authors.lastname: Lee
authors.forename: Jongcheol
authors.initials: J
authors.lastname: Seo
authors.forename: Dong Hun
authors.initials: DH
authors.lastname: Noh
authors.forename: Young Ho
authors.initials: YH
authors.lastname: Ko
authors.forename: Kimoon
authors.initials: K
authors.lastname: Kim
authors.forename: Hugh I
authors.initials: HI
authors.lastname: Kim